To evaluate more precisely the abilities of the electromagnetic (E.M.) Slingram method for magnetic features detection an experimental comparison was undertaken between the magnetic method with the best magnetometer now available (two optical pumping sensors in a differential mode) and the Slingram E.M. method with the SH3 apparatus, on the neolithic ring ditch at Viecht (Bavaria, F.R.G.). Despite the absence of automatic recording the electromagnetic results give the same archaeological information as that obtained by the magnetic method. -- AATA